We report 39 patients with non-Hodgkin's lymphoma who initially presented with ovarian enlargement. Fifteen patients had unilateral (10 left, four right, one unknown) and 24 had bilateral ovarian masses. The median size of the tumors was 8 cm (range, 2 to 23 cm). Histologically, using the Working Formulation, 21 lesions (54%) were classified as small noncleaved cell, Burkitt's type; 12 (31%) as large cell (nine diffuse, three focally follicular); three (8%) as diffuse mixed, small and large cell; two (5%) as large cell immunoblastic; and one (2%) as follicular and diffuse small cleaved cell. Twenty-six tumors were analyzed immunophenotypically, 25 (96%) of which were B-cell neoplasms. However, combining histologic and immunohistochemical findings, 37 neoplasms were of B-cell lineage, one diffuse large-cell lymphoma was not analyzed, and one large-cell immunoblastic lymphoma (with features of anaplastic large-cell lymphoma) was of T-cell lineage with an aberrant immunophenotype. On the basis of staging studies and clinical follow-up, we conclude that only four (10%) of the neoplasms in this study most likely arose in the ovary. The primary neoplasms, three diffuse large-cell and one diffuse mixed small- and large-cell, were B-cell neoplasms. Three of four patients with primary neoplasms were apparently cured at last follow-up following surgical excision and chemotherapy. The remainder of the lymphomas in this study, most commonly of small noncleaved cell, Burkitt's type, appear to be systemic tumors that involved the ovaries secondarily. Approximately 40% of patients with systemic neoplasms were alive without evidence of disease at last follow-up.